In a sputter ion pump, gases are pumped by being ionized and accelerated to a cathode and then either becoming embedded in the cathode material of the pump, being buried by cathode material sputtered by bombardment of the accelerated ions, or by chemical combination with the sputtered cathode material. The crossed electric and magnetic fields of the Penning cell or cells in the chamber of a sputter ion pump are utilized to provide a plasma discharge in the anode structure of the cell. Positive ions are produced in the discharge from the gases to be evacuated, and are accelerated by the electric field and bombard or react with a cathode structure of the cell or to sputter off cathode particles. The sputtered particles condense on other surfaces of the cathode structure, the anode structure or other surfaces inside the pump, and entrap ions through the various entrapment mechanisms to reduce pressure within the pump. These entrapment mechanisms include chemical combination for chemically active gases such as oxygen and nitrogen; electrical neutralization, burial and diffusion for small gas molecules such as hydrogen and helium; and electrical neutralization, burial and covering over with further sputtered deposits. The covering mechanism, also known as a capturing mechanism, is particularly suited for pumping noble gasses such as argon, neon, krypton and xenon.
The structure and operation of sputter ion pumps is well known. See, for example, U.S. Pat. Nos. 2,993,638, 3,319,875, 3,091,717 and 4,631,002. The electrical configurations of sputter-ion pumps include the “diode” configuration, in which a positive high voltage is applied to the anode structure and the cathode structure is maintained at ground potential, and the “triode” configuration, in which a negative high voltage is applied to the cathode structure and the anode structure is maintained at ground potential.
Nonevaporable getter pumps, or NEG pumps, are also well known. NEG pumps typically consist of a flange, heater and cartridge, and work by chemical reaction and phase change to sorb gases on the NEG material of the cartridge. Nonevaporable getter pumps are particularly suited for pumping non-noble gases such as hydrogen, nitrogen and oxygen.
It is common to operate sputter ion pumps and NEG pumps in tandem, although NEG ion pumps have been provided in which the housing of the pump is internally coated with a getter thin film.